Medical Malacology
Malacology derives from Ancient Greek μαλακός (malakós) which means soft, and -λογία (-logía) which means study. Malacology is the scientific study of the Phylum Mollusca (mollusks) which include snails, slugs, clams, cephalopods and other kinds many of which have shells. Fields within malacological research include taxonomy, ecology, and evolution. Applied malacology studies medical, veterinary, and agricultural applications.
The Egyptian Species of Freshwater Snails
Class: Gastropoda (snails)
Subclass1: Prosobranchia (gill breathing snails)
- Operculated snails with thick-walled shells.
Family1: Neritidae
- Hemispherical shell.
- Few whorls.
- Operculum with apophyses (processes).
- The Egyptian freshwater species is Theodoxus niloticus
Family2: Viviparidae
- Full-grown shell more than 10 mm in height.
- Dextral conical shell.
- The Egyptian freshwater species is Bellamya unicolor (note the presence of a keel).
Family3: Ampullaridae (Pilidae)
- Full-grown shell more than 15 mm in height.
- Dextral (Pila ovata) or sinistral shells (Lanistes carinatus).
- The Egyptian freshwater species are Pila ovata and Lanistes carinatus
Family4: Valvatidae
- Full-grown shell less than 10 mm in height.
- Shell wider than high.
- Circular operculum.
- The Egyptian freshwater species is Valvata nilotica
Family5: Hydrobiidae
- Full-grown shell less than 10 mm in height.
- Shell higher than wide.
- Ovate operculum.
- The Egyptian freshwater species are Hydrobia Ventrosa and Hydrobia musaensis
Family6: Bithyniidae
- Full-grown shell less than 15 mm in height.
- The aperture is fairly large, with a continuous thickened and often dark peristome.
- The operculum, which in full-grown specimens lodges to the peristome, has a spiral part occupying from 1/6 to 4/5 of the diameter.
- The Egyptian freshwater species is Gabbiella senaariensis
Family7: Thiaridae
- Full-grown shell more than 10 mm in height.
- Dextral (sculptured) shell.
- Basal margin of the aperture is entire.
- The Egyptian freshwater species are Melanoides (Melania) tuberculata and Cleopatra bulimoides
Family6: Potamididae
- Full-grown shell more than 10 mm in height
- Dextral sculptured shell.
- Basal margin of aperture with a notch.
- The Egyptian freshwater species is Pirenella conica
Subclass2: Pulmonata (air-breathing snails)
- Non-operculated snails with thin-walled shells.
Family1: Physidae
- Sinistral shell.
- Pseudobranch is absent.
- Colorless blood.
- The Egyptian freshwater species is Physa acuta
- Physa acuta can be differentiated from Bulinus truncatus by the following:
§ The shell is stronger, more conical, and pointed at the spire and whorls are without shoulder angle.
§ With twisted columella.
§ The body whorl has no umbilicus.
§ If you crush a living P. acuta a bluish fluid oozes out, instead of the reddish-colored fluid that comes out of B. truncatus snails.
§ The intermediate host of several species of bird trematodes, but is not related to human schistosomiasis.
Family2: Lymnaeidae
- Dextral shell.
- Pseudobranch is absent.
- Colorless blood.
- The Egyptian freshwater species are:
1- Lymnaea truncatula
- Small shell (up to 11 X 6 mm).
- The spire is equal in length to the aperture, and consists of 5-6 convex whorls.
- The intermediate host of F. hepatica.
2- Lymnaea natalensis (cailliaudi)
- Large shell (up to 23 X 15 mm).
- The spire is much shorter than the aperture, and consists of 4-4.4 whorls.
- The intermediate host of F. gigantica, and small snails may act as intermediate host of F. hepatica.
3- Lymnaea columella
- The shell (up to 17 X 9 mm) is narrower than L. natalensis and is easily distinguished from it by the close-set spiral lines, which result in a reticulated pattern.
- A possible intermediate host of F. hepatica.
4- Lymnaea stagnalis
- Large shell (45X 25 mm) with slender and sharply pointed spire.
- Young snails may act as an intermediate host of F. hepatica.
Family3: Planorbidae
- Pseudobranch is present.
- Red blood.
Subfamily1: Planorbinae
- Pseudodextral discoid or lentiform shell.
- The shell appears dextral, because it is carried inverted so that the side corresponding to the apical side in other snails is the lower side of the planorbin shell. Also, it may be considered as a dextral shell but with a sinistral animal.
- The Egyptian freshwater species are:
1- Planorbis planorbis
- Shell is more than 2 mm in height (2-3 mm).
- Distinct angle below the periphery.
2- Biomphalaria spp.
- Shell is more than 2 mm in height (3-6 mm).
- Prostatic duct and preputial gland are absent.
- Many species may serve as an intermediate host of S. mansoni.
Biomphalaria glabrata can be differentiated from Biomphalaria alexandrina by the following:
Widely umbilicate and has greater size.
§ B. alexandrina D: 16 mm and H: 5.6mm
§ B. glabrata D: 28 mm and H: 8 mm.
§ The number of whorls increases more rapidly in B. alexandrina than B. glabrata.
§ Unlike B. alexandrina, B. glabrata has a renal ridge.
3- Helisoma duryi
- The typical form can be distinguished from Biomphalaria spp. by :
§ Presence of prostatic duct and preputial gland.
§ Higher shell (up to 14 mm in height).
§ More regular whorls.
§ The flat surface within the umbilicus.
§ The deeply concave upper side.
4- Segmentorbis eussoensis
- Shell is less than 2mm in height.
- Lentiform shell with a convex upper side and flat underside.
- Shell with 3-9 sets of internal septa.
5- Gyraulus ehrenbergi
- Shell discoid flat on both sides.
- Full-grown shell less than 2mm in height, and in most cases with less than 5 rapidly increasing whorls.
- The shell often with an angle at the periphery.
6- Afrogyrus oasiensis
- Shell discoid flat on both sides.
- Full-grown shell less than 2mm in height, and in most cases with 5 slowly increasing whorls.
Subfamily2: Bulininae
- sinistral ovate or higher shell (except in one Asian species the shell is discoid).
- The Egyptian freshwater species are Bulinus truncatus (the intermediate host of S. haematobium) and Bulinus forskalii (the intermediate host of S. bovis).
For detailed information please refer to my publication: